EXCHANGE-INDUCED OPTICAL SPIN TRANSITIONS IN SEMIMAGNETIC SEMICONDUCTORS

Electron-spin flip by electric dipole light absorption in semimagnetic semiconductors (SMSC) is allowed not only by the generally invoked sp in-orbit coupling but also due to a possibility of exchange scattering of an electron by a magnetic impurity. The theory of such exchange-in duced electric dipole spin resonance (EDSR) in Mn- and Fe-based SMSC i s presented. Since exchange scattering changes the electron spin, as w ell as the impurity state, the bound-electron absorption occurs at the photon energy hBARomega = hBARomega(s) + epsilon(M), where hBARomega( s) is the electron giant spin splitting and epsilon(M) is an excitatio n energy of the magnetic impurity. In the case of Mn-based SMSC, epsil on(M) is SiMply the Zeeman energy of a Mn ion, while, since an Fe ion may be excited to a set of states, several absorption lines exist in F e-based SMSC. Exchange-induced EDSR differs from the conventional spin -orbit EDSR in the polarization and magnetic-field dependences of abso rption. For free carriers exchange-induced spin-flip absorption has no nresonant character and leads to a rather broad absorption band.